Hey,
Kinda struggling with Factorials, more precisely the process of adding and subtracting them. The question is 5! + 4!. Now, the back of the book says the answer is 6x4!, I just don't understand how you reach that conclusion, can anyone help me out?

Thanks

October 30th 2008, 09:12 AM

Chris L T521

Quote:

Originally Posted by scott.b89

Hey,
Kinda struggling with Factorials, more precisely the process of adding and subtracting them. The question is 5! + 4!. Now, the back of the book says the answer is 6x4!, I just don't understand how you reach that conclusion, can anyone help me out?

Thanks

Hello :)

Recall what a factorial is. When you take the factorial of a number, you take that number and multiply it by all the numbers preceding it.

For example,

Now to your question.

When you add , we see that this is the same as .

Looking at this closely, we notice that each term has a common factor:

.

So pull out the term , and we are left with .

But , so our answer is

Does this make sense?

--Chris

October 30th 2008, 01:25 PM

scott.b89

Thanks a lot, checked out the avatars on your page to. They're really good xD